The semi-active laser seeker is a mature technology used in various guided bombs, the HELLFIRE and COPPERHEAD missiles. In this technology, a laser designator shines a spot of laser light on the target. The seeker optical system collects laser energy reflected from the target and places it on a quadrant detector. The location of the laser spot in the field of view, and thus the location of the target, is determined by the ratio of energy on different quadrants of the detector.
The shortcoming of this technology is that for a reasonable field of regard, laser seekers in the current art are placed on a mechanical gimbal, which results in significant costs and potential reliability issues due to complexity and moving parts. Attempts to do strapdown seekers without gimbals results in the field of regard and the field of view being the same, and such seekers typically work only in narrow fields of view.
The range at which a target is detected depends on energy collected, but wide fields of view in conventional optics result in small optics, thus small amounts of energy is collected resulting in shorter detection ranges. Attempts to make the optics large result in more optical aberrations for off-axis targets. Here, the spot on the detector representative of a target becomes increasingly blurred as the spot moves toward the edge of the optics, decreasing energy on the detector. Such a change in energy with increasing angle is known as the “transfer curve”, and can become very small with increasing angle. This results in high angular noise.
The instant invention provides a novel and unobvious, yet simple and elegant, solution to these problems by providing a combination of a wide field of view and an energy collection capability that is nearly independent of viewing angle over the field of view of the optical system. These enhanced capabilities are provided in a seeker assembly that may be implemented as a strapdown sensor with no moving parts, thus offering substantial benefits in decreased costs and increased reliability.